In machining, the factor which plays a major role in shortening the processing time and minimizing the strain due to processing is to enhance contact lubrication between a cutting tool or grinding tool and a workpiece and promote dissipation of heat of friction or cooling. That is, from the standpoint that the cutting conditions can be improved by slightly weakening the surface layer, if the coolant liquid is allowed to flow in all directions into the main cutting shear region and to be adsorbed by the created macroscopic cracks or voids, this results in lowering the surface energy and preventing re-adhesion. Such effect of brittleness in the shear region is very useful in providing an increased shear angle and a decrease in the thickness of chips and also in the cutting force. On the other hand, since tools transiently create a field of plastic deformation and shear in the surface of a workpiece, it is of utmost importance that effective cooling and lubrication be effected for each transient field of plastic deformation and shear with which the tool comes in contact.
However, in conventional machine tools, a coolant liquid fed directly to such transient field (tool contact region) through a nozzle is flung away by the rotation of the tool or workpiece and only superficially passes along the tool and workpiece surfaces; therefore, it can hardly be said that the coolant liquid contributes to effective cooling and lubrication.